nixos: create 'modules/nixos' folder

Let's consolidate all modules under one path, so that NixOS,
home-manager, and nix-darwin (if I ever end up using it down the line)
would go under the same folder.

modules/nixos/services/quassel/default.nix

@@ -0,0 +1,50 @@
+# An IRC client daemon
+{ config, lib, ... }:
+let
+  cfg = config.my.services.quassel;
+  domain = config.networking.domain;
+in
+{
+  options.my.services.quassel = with lib; {
+    enable = mkEnableOption "Quassel IRC client daemon";
+    port = mkOption {
+      type = types.port;
+      default = 4242;
+      example = 8080;
+      description = "The port number for Quassel";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    services.quassel = {
+      enable = true;
+      portNumber = cfg.port;
+      # Let's be secure
+      requireSSL = true;
+      certificateFile = config.security.acme.certs."${domain}".directory + "/full.pem";
+      # The whole point *is* to connect from other clients
+      interfaces = [ "0.0.0.0" ];
+    };
+
+    # Allow Quassel to read the certificates.
+    users.groups.acme.members = [ "quassel" ];
+
+    # Open port for Quassel
+    networking.firewall.allowedTCPPorts = [ cfg.port ];
+
+    # Create storage DB
+    services.postgresql = {
+      enable = true;
+      ensureDatabases = [ "quassel" ];
+      ensureUsers = [
+        {
+          name = "quassel";
+          ensurePermissions."DATABASE quassel" = "ALL PRIVILEGES";
+        }
+      ];
+      # Insecure, I don't care.
+      # Because Quassel does not use the socket, I simply trust its connection
+      authentication = "host quassel quassel localhost trust";
+    };
+  };
+}